青藏高原东北部天然地震探测与岩石圈深部特征

为了研究青藏高原东北部块体构造变形的深部驱动机制, 笔者对青藏高原东北部的天然地震观测数据进行地震层析反演,并结合同一剖面的接收函数及各向异性结果进行讨论 .介绍了ACH方法的基本原理,论述了由于印度板块向北俯冲的强大的持续作用力,造就了NE向俯冲到柴达木盆地之下的昆仑造山带,并发现在巴颜喀拉地体下方壳幔内的仰冲活动.壳幔内的低速体十分显著地出现在阿尼玛卿缝合线以北,深度可达300 km.推断该低速体可能与昆仑断裂在深层的剪切作用有关.深部资料显示该区莫霍界面由北向南逐渐加深,这与青藏高原东北部的岩石圈减薄现象一致,而且与印度板块向北运动的远程效应有关 .另外,地震层析结果及各向异性分析也支持青藏高原东北部主应力方向转为NE向的观点.     

Inverse compton scattering in anisotropic synchrotron sources

Models of compact, high brightness temperature sources such as quasars and active galactic nuclei often predict substantial inverse-compton scattered flux to be produced at high frequencies. As these fluxes are not observed, it is necessary to assume that extreme relativistic and/or anisotropic effects dominate the source. The often used equations to include these effects however are derived with several simplifying assumptions, which may not always be consistent with the derived source parameters (for example, the assumption of no time dependence in a violently variable quasar may not be appropriate). We therefore present here an explicit derivation of the dependence of the rate of inverse compton scattering on anisotropies in the source, to emphasise the importance and number of assumptions required in the derivation.     

The impact of aquifer stratification on saltwater intrusion characteristics. Comprehensive laboratory and numerical study

Laboratory experiments and numerical simulations were utilized in this study to assess the impact of aquifer stratification on saltwater intrusion. Three homogeneous and six layered aquifers were investigated. Image processing algorithms facilitated the precise calculation of saltwater wedge toe length, width of the mixing zone, and angle of intrusion. It was concluded that the length of intrusion in stratified aquifers is predominantly a function of permeability contrast, total aquifer transmissivity and the number of heterogeneous layers, being positively correlated to all three. When a lower permeability layer overlays or underlays more permeable zones its mixing zone widens, while it becomes thinner for the higher permeability strata. The change in the width of the mixing zone (WMZ) is positively correlated to permeability contrast, while it applies to all strata irrespectively of their relative vertical position in the aquifer. Variations in the applied hydraulic head causes the transient widening of WMZ. These peak WMZ values are larger during saltwater retreat and are negatively correlated to the layer's permeability and distance from the aquifer's bottom. Moreover, steeper angles of intrusion are observed in cases where low permeability layers overlay more permeable strata, and milder ones in the inverse aquifer setups. The presence of a low permeability upper layer results in the confinement of the saltwater wedge in the lower part of the stratified aquifer. This occurs until a critical hydraulic head difference is applied to the system. This hydraulic gradient value was found to be a function of layer width and permeability contrast alike.     

Phytopigments and fatty acids in the gut of the deposit-feeding heart urchin Echinocardium cordatum in the southern North Sea: Selective feeding and its contribution to the benthic carbon budget

As part of a broader study on benthic-pelagic coupling in the southern North Sea, specimens of the common heart urchin Echinocardium cordatum were sampled for analyses on phytopigments and fatty acids in their guts. Results were interpreted in the context of feeding and ecological functioning of the heart urchins in the benthic system. Ingestion selection factors for both component groups were relatively high, 5 to 9 for chlorophyll a and 9 to 130 for total fatty acids. The data point to at least partially different sources of the pigments and of the fatty acids. Next to algal detritus, small infauna relatively rich in fatty acids might be preferentially co-ingested with the detritus. Due to digestive breakdown and absorption, the concentrations of pigments and fatty acids were importantly decreased, indicating a rather high digestion efficiency for this subsurface deposit feeder, up to 80%. The results indicate that E. cordatum increases its energy acquisition by strong selectivity and a high digestive efficiency. Optimal foraging is likely to apply on deposit-feeding invertebrates in relatively food-rich coastal environments as much as it does in the food-poor deep-sea environment. Using chlorophyll a as a proxy for carbon, the contribution of the urchin population to the momentary benthic carbon budget was calculated at 7% to 42%.     

The response of soil erosion and sediment export to land-use change in four areas of Europe: The importance of landscape pattern

The response of erosion and sediment export to past land-use change has been studied in four agricultural areas of Europe. Three of these areas were subject to land abandonment or de-intensification and one to intensification of land-use practices. Erosion and sediment yield were modeled using the WaTEM/SEDEM model, which combines the RUSLE equation with a sediment routing algorithm. Spatial relationships between the RUSLE C-factor (i.e. land-use) and other erosion and sediment export-determining factors (slope, soil erodibility and distance to rivers) were investigated, as these account for non-linearity in the response of erosion and sediment export to land-use change.Erosion and sediment export have decreased enormously in the de-intensified areas, but slightly increased in the intensively cultivated area. The spatial pattern of land-use change in relation to other erosion and sediment export-determining factors appears to have a large impact on the response of soil erosion and sediment export to land-use change. That the drivers of abandonment of arable land and erosion coincide indicates that de-intensification leads to a more favourable landscape pattern with respect to reduction of erosion and sediment export. This mechanism applies not only within the study areas, but also among the European study areas where the process of intensification of some areas and de-intensification of others might result in an overall decrease of erosion and sediment yield through time.     

Exploring for Geothermal Resources with Electromagnetic Methods

Electrical conductivity of the subsurface is known to be a crucial parameter for the characterization of geothermal settings. Geothermal systems, composed by a system of faults and/or fractures filled with conducting geothermal fluids and altered rocks, are ideal targets for electromagnetic (EM) methods, which have become the industry standard for exploration of geothermal systems. This review paper presents an update of the state-of-the-art geothermal exploration using EM methods. Several examples of high-enthalpy geothermal systems as well as non-volcanic systems are presented showing the successful application of EM for geothermal exploration but at the same time highlighting the importance of the development of conceptual models in order to avoid falling into interpretation pitfalls. The integration of independent data is key in order to obtain a better understanding of the geothermal system as a whole, which is the ultimate goal of exploration.